Method for Making a Sensor Device Using a Graphene Layer

ABSTRACT

A graphene layer is generated on a substrate. A plastic material is deposited on the graphene layer to at least partially cover the graphene layer. The substrate is separated into at least two substrate pieces.

This is a continuation application of U.S. application Ser. No.14/289,512, issued on Jun. 30, 2015 as U.S. Pat. No. 9,070,615, entitled“Method for Making a Sensor Device Using a Graphene Layer” which wasfiled on May 28, 2014 which is a divisional application of U.S.application Ser. No. 13/226,173, issued on Jun. 24, 2014 as U.S. Pat.No. 8,759,153, entitled “Method for Making a Sensor Device Using aGraphene Layer” which was filed on Sep. 6, 2011, both of whichapplications are incorporated herein by reference.

TECHNICAL FIELD

This invention relates to an electronic device including a sensor, andin particular, to an electronic device including a fluid, chemical orbiocomponent sensor.

BACKGROUND

In the development of devices including sensors special requirements maybe taken into account, in particular, when designing the sensitivity andthe package of a sensor device. For example, certain sensors, such asfluid, chemical or biocomponent sensors, may require an opening throughwhich the substance which is to be detected is applied to the sensor.Such packages may become large, sophisticated and expensive. However,both the manufacturers and the consumers of electronic devices desiredevices that are inexpensive, reduced in size and yet have increaseddevice functionality.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of embodiments and are incorporated in and constitute apart of this specification. The drawings illustrate embodiments andtogether with the description serve to explain principles ofembodiments. Other embodiments and many of the intended advantages ofembodiments will be readily appreciated as they become better understoodby reference to the following detailed description. The elements of thedrawings are not necessarily to scale relative to each other. Likereference numerals designate corresponding similar parts.

FIGS. 1A to 1C schematically illustrate cross-sectional views of oneembodiment of a method;

FIG. 2 schematically illustrates a cross-sectional view of oneembodiment of a sensor device;

FIGS. 3A and 3B schematically illustrate cross-sectional views ofembodiments of a sensor device;

FIG. 4 schematically illustrates a cross-sectional view of oneembodiment of a sensor device;

FIG. 5 schematically illustrates a cross-sectional view of oneembodiment of a sensor device;

FIG. 6 schematically illustrates a cross-sectional view of oneembodiment of a sensor device;

FIGS. 7A to 7E schematically illustrate cross-sectional views of oneembodiment of a method to produce a sensor device;

FIGS. 8A to 8E schematically illustrate cross-sectional views of oneembodiment of a method to produce a sensor device;

FIG. 9 schematically illustrates a cross-sectional view of oneembodiment of a sensor device;

FIGS. 10A to 10D schematically illustrate cross-sectional views of oneembodiment of a method to produce a sensor device;

FIG. 11 schematically illustrates a cross-sectional view of oneembodiment of a sensor device;

FIG. 12 schematically illustrates a cross-sectional view of oneembodiment of a sensor device;

FIGS. 13A to 13M schematically illustrate cross-sectional views of oneembodiment of a method to produce a sensor device;

FIG. 14 schematically illustrates a top view of the structureillustrated in FIG. 13G; and

FIG. 15 schematically illustrates a cross-sectional view of oneembodiment of a sensor device.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

In the following detailed description, reference is made to theaccompanying drawings, which form a part hereof, and in which is shownby way of illustration specific embodiments in which the invention maybe practiced. In this regard, directional terminology, such as “top,”“bottom,” “front,” “back,” “leading,” “trailing,” etc., is used withreference to the orientation of the figures being described. Becausecomponents of embodiments can be positioned in a number of differentorientations, the directional terminology is used for purposes ofillustration and is in no way limiting. It is to be understood thatother embodiments may be utilized and structural or logical changes maybe made without departing from the scope of the present invention. Thefollowing detailed description, therefore, is not to be taken in alimiting sense, and the scope of the present invention is defined by theappended claims.

It is to be understood that the features of the various exemplaryembodiments described herein may be combined with each other, unlessspecifically noted otherwise.

As employed in this Specification, the terms “coupled” and/or“electrically coupled” are not meant to mean that the elements must bedirectly coupled together; intervening elements may be provided betweenthe “coupled” or “electrically coupled” elements.

Embodiments of devices which may contain semiconductor chips aredescribed below. The semiconductor chips may be of different types, maybe manufactured by different technologies and may include, for example,integrated electrical, electro-optical or electro-mechanical circuitsand/or passives. The semiconductor chips may, for example, be designedas logic integrated circuits, analog integrated circuits, mixed signalintegrated circuits, memory circuits or integrated passives. They mayinclude control circuits, microprocessors or microelectro-mechanicalcomponents. The semiconductor chips need not be manufactured fromspecific semiconductor material, for example, Si, SiC, SiGe, GaAs,AlGaAs and, furthermore, may contain inorganic and/or organic materialsthat are not semiconductors, such as, for example, insulators, plasticsor metals.

The sensor devices described below may include external contact elementssuch as, e.g., leads or solder deposits or contact pads on a package.The external contact elements may represent the external terminals ofthe package. They may be accessible from outside the package and maythus allow electrical contact to be made with the device from outsidethe package. Furthermore, the external contact elements may be thermallyconductive and may serve as heat sinks for dissipating the heatgenerated by the semiconductor chip or chips embedded in thesemiconductor package. The external contact elements may be composed ofany desired electrically conductive material, for example, of a metal,such as copper, aluminum or gold, a metal alloy or an electricallyconductive organic material. Solder deposits, such as solder balls orsolder bumps, may represent the external contact elements or may bedeposited on the external contact elements.

The sensor devices may comprise an encapsulating material to form anencapsulation body (e.g., a molded body), which may be electricallyinsulating. The encapsulating material may be a dielectric material andmay be made of any appropriate duroplastic, thermoplastic orthermosetting material or laminate (prepreg). The encapsulating materialmay contain filler materials. After its deposition, the encapsulatingmaterial may be only partially hardened and may be completely hardenedafter application of energy (e.g., heat, UV light, etc.) to form anencapsulation body. Various techniques may be employed to cover thesemiconductor chips with the encapsulation body, for example,compression molding, injection molding, powder molding, liquid molding,dispensing or laminating.

In one embodiment, the encapsulation body may be used to produceso-called fan-out type packages. In a fan-out type package at least someof the external contact pads and/or conductor traces connecting thesemiconductor chip to the external contact pads are located laterallyoutside of the outline of the semiconductor chip or do at leastintersect the outline of the semiconductor chip. Thus, in fan-out typepackages, a peripherally outer part of the package of the semiconductorchip is typically (additionally) used for electrically bonding thepackage to external applications, such as, e.g., application boards or,in stacked package applications, another package. This outer part of thepackage encompassing the semiconductor chip effectively enlarges thecontact area of the package in relation to the footprint of thesemiconductor chip, thus leading to relaxed constraints in view ofpackage pad size and pitch with regard to later processing, e.g., secondlevel assembly.

A graphene layer is generated on a substrate (e.g., wafer or artificialwafer or other carrier). The graphene layer may be applied on thesubstrate before separating the substrate into individual devices. Byway of example, if the substrate is a wafer, the graphene layer may begenerated on the wafer during wafer level processing, that is duringfrontend processing.

The graphene layer may be applied by a spin coating process. Further,the graphene layer may be applied by micro-mechanical cleavage ofgraphite or by a CVD (Chemical Vapor Deposition) process. By way ofexample, spin-coated graphene films may be produced by chemicaloxidation and exfoliation of graphite to produce graphite oxide, itssubsequent reduction to graphene by using, e.g., liquid anhydroushydrazine as a reducing agent and solvent for dispersion of large, highquality graphene flakes, and by depositing this material using acentrifuged solution to achieve well dispersed, single layer grapheneflakes.

FIGS. 1A to 1C schematically illustrate one embodiment of a method togenerate a sensor device 100 as shown in FIG. 2. According to FIG. 1A, asubstrate 1 is provided. The substrate 1 may have the form of a plate.It may be made of different kinds of material. By way of example, thesubstrate 1 may be a semiconductor wafer, a so-called artificial waferor a plate made of plastics such as, e.g., polyimide.

A graphene layer 2 is deposited on one main surface of the substrate 1.In one embodiment the graphene layer 2 may be an unstructured layerwhich may completely cover the respective main surface of the substrate1. In another embodiment the graphene layer 2 may be generated as astructured layer which only partly covers the respective main surface ofthe substrate 1.

A plastic material 3 is deposited over the graphene layer 2 (FIG. 1C).The plastic material 3 may completely or partially cover the graphenelayer 2. In one embodiment, the plastic material 3 may be deposited in apre-structured, patterned form on the graphene layer 2 to only coverspecific zones of the graphene layer 2. Further, in one embodiment, theplastic material 3 may be deposited as an unstructured, continuous layerand may then be structured to only cover specific zones of the graphenelayer 2.

The plastic material 3 may be made of a material which selectivelycontrols the exposure of the covered zone of the graphene layer 2 withsubstances of the environment. The selection of the plastic material 3depends on the desired functionality of the sensor device to befabricated. Depending on the selected plastic material 3 and itsspecificity to different substances, the sensor device will be sensitiveto different substances.

By way of example, chemical sensors sensitive to specific elements ormolecules such as, e.g., CO₂, H₂O, NO₂, NH₃, etc. may be provided.Further, biocomponent sensors sensitive to, e.g., DNA, microbes,specific cells, the content of oxygen in blood, etc., may be provided.Still further, fluid sensor devices such as, e.g., gas sensors or liquidsensors may be provided, e.g., to sense one or more of the substancesmentioned above.

In one embodiment, the plastic material 3 may comprisepolyethylenterephtalate. The permeability of polyethylenterephtalateagainst CO₂ is more than one order of magnitude greater than thepermeability of polyethylenterephtalate against O₂, carbon hydrides orH₂O. That way, the selectivity of a CO₂ sensor may be significantlyincreased.

In one embodiment, the plastic material 3 may comprise polyvinylidenechloride. Polyvinylidene chloride may increase the sensitivity of ahumidity sensor against O₂ and CO₂ by more than three orders ofmagnitude. Further, there are a great variety of other materials whichprovide different permeabilities and thus selectivities for variousspecific chemical elements, molecules, biocomponents or othersubstances.

In one embodiment (not illustrated in FIGS. 1A to 1C) the graphene layer2 may be structured before depositing the plastic material 3 on thegraphene layer 2.

In one embodiment (not shown in FIGS. 1A to 1C) the graphene layer 2 maybe structured after depositing the plastic material 3 on the graphenelayer 2 by using the deposited plastic material 3 as a mask. Both thesepossible processes of structuring the graphene layer 2 will be explainedwith reference to embodiments further below.

The plastic material 3, which is also referred to in the art as a globtop material, may be deposited on the graphene layer 2 by, e.g., adispensing, printing or CVD process. In one embodiment the plasticmaterial 3 is deposited in a pre-structured form on the graphene layer2. By way of example, dispensing or printing processes are available todeposit structures such as, e.g., islands of plastic material 3 on thegraphene layer 2. In one embodiment the plastic material 3 is depositedon the graphene layer 2 as an unstructured, continuous layer. In thisembodiment, the structuring of the plastic material 3 on the graphenelayer 2 may be provided by using photo-lithographic methods and/oretching methods.

As illustrated in FIG. 1C, sensor devices 100 are then separated fromone another by separation of the substrate 1 and possibly the graphenelayer 2 and the plastic material 3. By way of example, sawing, cutting,etching or laser beams may be used for the separation step.

The operational principle of the graphene sensor devices described belowis based on changes in their electrical conductivity (or resistance) dueto substances absorbed on the surface of the graphene layer 2 extendingbelow the plastic material 3. The electrical conductivity (orresistance) of the graphene layer 2 is highly sensitive to adsorbates,with the kind of adsorbates reaching the graphene's surface beingcontrolled by the composition of the plastic material 3 as explainedabove. Further, the selectivity of graphene to different substances maybe controlled by adjustable surface chemistry of the graphene layer 2.In this connection it is to be noted that the term graphene as usedherein is to be understood in a broad meaning. In particular, it isintended that the term graphene may also comprise graphene-based layerswith modifiable chemical functionality such as graphene derivativesand/or so-called chemically modified graphenes.

The changes in electrical conductivity or resistance of the graphenelayer 2 covered by the plastic material 3 may be sensed by at least twoelectrical contacts applied to the graphene layer 3. By way of example,FIGS. 3A and 3B illustrate two electrical contacts 11 applied to thegraphene layer 2, with the electrical contacts 11 being arranged in aspaced apart relationship. In one embodiment (FIG. 3A) the electricalcontacts 11 are deposited on the upper surface of the graphene layer 2.In one embodiment (FIG. 3B) the electrical contacts 11 are provided toconnect to the lower surface of the graphene layer 2. In bothembodiments, the electrical contacts 11 are located such that the lengthof the graphene layer 2 in between the electrical contacts 11 iscompletely covered by the diffusion-selective plastic material 3. Theprinciples illustrated in the embodiments of FIGS. 3A and 3B areapplicable to other embodiments described herein.

FIG. 4 illustrates a cross-sectional view of one embodiment of a sensordevice. In this embodiment, the sensor device 100 is encapsulated in anencapsulation body 14. The encapsulation body 14 has an opening 17 toexpose the plastic material 3 to the environment.

As will be explained further below in greater detail, the encapsulationbody 14 may be fabricated by way of molding (for example, compressionmolding, injection molding, granulate molding, powder molding or liquidmolding). Typically, in a molding process a lower mold half and an uppermold half are used to define a cavity in which the encapsulation body 14is formed.

In one embodiment the opening 17 to expose the plastic material 3 isformed during the molding process. By way of example, the upper moldhalf may be provided with a dome or post protruding into the mold cavityand pressing onto the upper surface of the plastic material 3. That waythe opening 17 may be recessed by the dome of the molding tool. Inanother embodiment the opening 17 may be generated after the moldingprocess and the formation of the encapsulation body 14 by machining,e.g., by mechanical or laser drilling or milling.

FIG. 5 illustrates a cross-sectional view of one embodiment of a sensordevice. In this sensor device the sensor device 100 is accommodated in ahollow housing 18 made of, e.g., plastic. Similar to the embodimentillustrated in FIG. 4, the hollow housing 18 has an opening 17 to exposea part of the upper surface of the plastic material 3. The walls of theopening 17 may tightly connect to the upper surface of the plasticmaterial 3 in order to avoid any substances of the environment to enterthe space within the hollow housing 18.

FIG. 6 illustrates a cross-sectional view of one embodiment of a sensordevice. In this embodiment the sensor device 100 is covered by alaminate material 19 encapsulating the upper surface of the sensordevice 100. The laminate material may be a polymer foil having anopening 17. Again, similar to the embodiments illustrated in FIGS. 4 and5, the opening 17 exposes a part of the surface of the plastic material3.

In one embodiment the laminate material 19 may be laminated onto thestructure shown in FIG. 1C before separating the substrate 1 intoindividual sensor devices 100. In this case the laminate material 19 mayhave a pattern of openings 17 aligned to the pattern of plastic material3 and/or sensor devices 100 to be separated from the structure shown inFIG. 1C.

It is to be noted that in the embodiments of FIGS. 4 to 6 the sensordevices 100 may be equipped with electrical contacts 11 as illustratedin FIG. 3A and/or FIG. 3B.

The functionality of the sensor device 100 may significantly depend onthe design of the substrate 1. If the substrate 1 comprises asemiconductor chip including an integrated circuit, the variations ofthe electric conductivity or resistance sensed by the electricalcontacts 11 may directly be measured and, if desired, processed by theintegrated circuit. To this end, the integrated circuit may compriseanalog circuitry such as, e.g., a testing bridge, digital circuitry suchas, e.g., logic circuitry, semiconductor memory, input/output circuitry,and/or mixed circuitry. Further, the substrate 1 may comprise a heaterand/or a temperature receiving element and/or a control circuitry forcontrolling the heater in response to the output of the temperaturereceiving element. The heater, the temperature receiving element and thecontrol circuitry may each be implemented in a semiconductor chipcontained in the substrate 1 or off-chip.

In one embodiment the substrate 1 is a plastic plate as, for example, isused in a chip card or smart card. By way of example, the embodiment ofFIG. 6 may illustrate a chip card or smart card designed as orcontaining a sensor device. In such a smart card or chip card thegraphene layer 2 may either be deposited over the semiconductor chip(not illustrated) embedded in the plastic plate or may be deposited overthe plastic plate as such, e.g., a polyimide plate. In the latter caseconductor traces on the plastic plate or dielectric substrate may beused to electrically connect to the graphene layer 2. It is to be notedthat it is also possible to use a plastic plate as substrate 1 withoutany semiconductor chip embedded therein. The conductivity of thegraphene layer 2 may, in this case, be measured by external devicesdesigned to make contact to external electrodes on the card which arecoupled, e.g., by conductor traces to the graphene layer 2.

FIGS. 7A to 7E schematically illustrate a method for manufacturing asemiconductor device 200 as shown in FIG. 7E, or, if mounted on a board,in FIG. 9. The method illustrated in FIGS. 7A to 7E is an implementationof the method shown in FIGS. 1A to 1C. The details of the productionmethod that are described below can therefore be likewise applied to themethod illustrated in FIGS. 1A to 1C. Vice versa, the details describedin conjunction with FIGS. 1A to 1C are likewise applicable to the methodof FIGS. 7A to 7E. Furthermore, the semiconductor device 200 is animplementation of the semiconductor device 100. The details of thesemiconductor device 200 that are described below can therefore belikewise applied to the semiconductor device 100, and vice versa.

In the embodiment shown in FIGS. 7A to 7E, the substrate 1 is a wafer 20made of semiconductor material. The semiconductor wafer 20 may include abulk silicon in which integrated circuits are embedded. Chip contactpads referred to in the following as chip electrodes 21 are located on afirst main face 22 of the semiconductor wafer 20. The chip electrodes 21correspond to the electrical contacts 11 of the embodiment shown in FIG.3B. The integrated circuits embedded in the semiconductor wafer 20 canbe electrically accessed via the chip electrodes 21. The chip electrodes21 may be made of a metal, for example, aluminum or copper, and may haveany desired shape and size. It is to be noted that the chip electrodes21 illustrated in FIGS. 7A to 7E are chip electrodes intended to becoupled to a graphene layer 2 to sense the conductivity or resistancethereof. However, the semiconductor wafer 20 may be provided with otherchip electrodes not shown in FIGS. 7B to 7E intended to be used, e.g.,for power supply, I/O circuitry, heater, temperature receiving element,etc.

A structured insulating layer 23 may be generated on the first main face22 of the semiconductor wafer 20 as illustrated in FIG. 7A. Theinsulating layer 23 may be fabricated in various ways. For example, theinsulating layer 23 may be deposited from a gas phase or from asolution, or can be laminated onto the first main face 22. Furthermore,thin-film technology methods can be used for the application of theinsulating layer 23. The insulating layer 23 may be fabricated from apolymer, such as parylene, photoresist material, imide, epoxy,duroplast, silicone. The thickness of the insulating layer 23 may be upto 10 μm or even higher. The insulating layer 23 may also be a hardpassivation layer of, e.g., silicon dioxide, silicon nitride or of aninorganic, ceramic-like material, such as silicon-carbon compounds.

In order to electrically connect to the integrated circuits embedded inthe semiconductor wafer 20, the insulating layer 23 may be opened inareas where the chip electrodes 21 are arranged as illustrated in FIG.7A. The openings 24 in the insulating layer 23 may, for example, beproduced by using photolithographic methods and/or etching methods. Itis to be noted that lands, stripes or circles 25 of the insulating layer23 may remain on at least some of the chip electrodes 21 and may, e.g.,be located in a central part of the chip electrodes 21.

FIG. 7B illustrates the deposition of a graphene layer 2. The graphenelayer 2 may be deposited as an unstructured, continuous layer at waferlevel. Thus, the graphene layer 2 may be deposited on the insulatinglayer 23 and on the chip electrodes 21 exposed by the openings 24 of theinsulating layer 23, and can make electrical contact to the chipelectrodes 21. The deposition process of the graphene layer 2 may beidentical or similar to one or more of processes described above withreference to other embodiments. Therefore, reiteration of thecorresponding descriptions is omitted for the sake of brevity.

The graphene layer 2 may then be structured as shown in FIG. 7C. In oneembodiment, a photoresist layer may be deposited, for example,spin-coated, on top of the graphene layer 2 (not illustrated). Byexposure to light having a suitable wavelength through a mask andsubsequent development, recesses are formed in the photoresist layer.Subsequently, if the photoresist material is of a positive tone, theportions of the graphene layer 2 that are exposed by the recesses may beremoved by using an appropriate solvent or etching agent, e.g., by usingan O₂ plasma etching method. If the photoresist material is of anegative tone, all not exposed areas are removed by the solvent oretching agent. The remaining portions of the graphene layer 2 may becontinuous between each two chip electrodes 21 associated with each oneof the integrated circuits embedded in the semiconductor wafer 20, andmay have recesses elsewhere.

According to FIG. 7D, a plastic material 3 is deposited over theremaining portions of the graphene layer 2. This step corresponds to theprocess described in conjunction with FIG. 1C, and reference is madethereto in order to avoid reiteration. In one embodiment, the plasticmaterial 3 may completely cover and hermetically seals the remainingportions of the graphene layer 2. In one embodiment, the plasticmaterial 3 at least covers the remaining portions of the graphene layer2 over the length where it extends between the chip electrodes 21. Inboth cases, substances of the environment adsorbing on the graphenelayer 2 at a location between the two chip electrodes 21 have topenetrate the diffusion-selective plastic material 3.

As already mentioned in relation to other embodiments, the deposition ofthe plastic material 3 may be accomplished in a pre-structured manner,e.g., by dispensing or printing. If the plastic material 3 is depositedin a pre-structured manner, remaining parts of the insulating layer 23may assist the deposition process. By way of example, if the plasticmaterial 3 deposited on the semiconductor wafer 20 is a viscous liquid,the lands, stripes or circles 25 of the insulating layer 23 may act asbarriers to prevent the liquid from distributing over the surface of thesemiconductor wafer 20. That way, the lands, stripes or circles 25,together with the viscosity of the liquid plastic material 3, mayguarantee a minimum height of, e.g., more than 10, 50 or even 100 μm ofthickness of the plastic material 3 over the length where it extendsbetween the chip electrodes 21. That way, the selectivity of the plasticmaterial 3 may be improved or a minimum selectivity be set.

As illustrated in FIG. 7E, the semiconductor wafer 20 may then besingulated into individual semiconductor chips 30, for example, bysawing, cutting, etching or laser ablation, e.g., stealth dicing. Onlythree of these semiconductor chips 30 are illustrated in FIG. 7E. Thesemiconductor chip 30 illustrated in FIG. 7E may be one specificimplementation of the piece of substrate 1 shown in FIG. 2.

Solder deposits 26 may be placed onto the chip electrodes 21 asillustrated in FIG. 7E. The solder deposits 26 may be applied to thechip electrodes 21 by so-called “ball placement”, in which pre-shapedballs composed of solder material are applied to the chip electrodes 21.As an alternative to “ball placement”, the solder deposits 26 may, forexample, be applied by means of stencil printing with a solder paste,followed by a heat-treatment process. The solder material may be formedfrom metal alloys which are composed, for example, from the followingmaterials: SnPb, SnAg, SnAgCu, SnAgCuNi, SnAu, SnCu and SnBi.

In one embodiment, the solder deposits 26 are applied on wafer level,i.e., prior to the step of singulating the semiconductor wafer 20 intoindividual semiconductor chips 30.

In one embodiment, the solder deposits 26 are applied on the individualsemiconductor chips 30, i.e., after the step of singulating thesemiconductor wafer 20 into semiconductor chips 30.

In one embodiment, the solder deposits 26 are attached to the chipelectrodes 21 which make direct electrical contact to the graphene layer2. This allows direct external access to the graphene layer 2.Additional solder deposits 26 may be attached to chip electrodes 21which are not directly connected to the graphene layer 2 (notillustrated).

In one embodiment, the solder deposits 26 are attached only to chipelectrodes 21 which do not make direct electrical contact to thegraphene layer 2 (not illustrated). In this case, in particular, theintegrated circuit formed in the semiconductor chip 30 typicallycomprises a sensing or measuring circuitry and/or an evaluationcircuitry and/or an I/O circuitry. Of course, one or more of thesecircuitry may also be contained in a semiconductor chip 30 of theaforementioned embodiments.

The solder deposits 26 may be used to electrically couple the device 200to other components, see FIG. 9.

FIGS. 8A to 8E schematically illustrate one embodiment of a method toproduce a semiconductor device 200. The method steps shown in FIGS. 8Aand 8B correspond to the method steps in FIGS. 7A and 7B, and referenceis made to the corresponding description.

According to FIG. 8C, the plastic material 3 is deposited on thecontinuous (i.e., unstructured) graphene layer 2. Deposition of theplastic material 3 may be accomplished in the same way as described inconjunction with FIG. 7D.

According to FIG. 8D, the graphene layer 2 is structured. In thisembodiment the plastic material 3 (also referred to as a glob topmaterial in the art) is used as a mask for structuring the graphenelayer 3. That is, the regions of the graphene layer 2, which are notcovered by the plastic material 3, may be removed by a solvent oretching agent. By way of example, an O₂-plasma etching process may beused. As a result, the design or pattern of the remaining portions ofthe graphene layer 2 is in conformity to the design or pattern of theplastic material 3 (FIG. 8D). The provision of the plastic material 3 asa mask for structuring the graphene layer 2 guarantees that the graphenelayer 2 is completely covered and sealed by the plastic material 3.

As illustrated in FIG. 8E, the semiconductor wafer 20 may then besingulated into semiconductor chips 30. This method step is analogous tothe method step illustrated in FIG. 7E, and reference is made to theaccompanying description in order to avoid reiteration.

FIG. 9 illustrates a cross-sectional view of sensor device 200 mountedon a carrier 40 such as, e.g., a PCB (Printed Circuit Board). Here, byway of example, the sensor device 200 is mounted on the carrier 40 in aflip-chip orientation. The sensor device 200 is the finished sensordevice, and is also referred to as a wafer level package in the art.

FIGS. 10A to 10D illustrate one embodiment of a method to produce asensor device 300, a cross-section of which is illustrated in FIG. 10D.In order to manufacture the sensor device 300, a leadframe 50 may beprovided which is illustrated in FIG. 10B in cross-section. Theleadframe 50 may include one or more die pads 51 and a plurality ofleads 52. The leadframe 50 may be manufactured from a metal or metalalloy, in particular copper, a copper alloy, iron, nickel, aluminum, orother appropriate materials. Furthermore, the leadframe 50 may be platedwith an electrically conductive material, for example, copper, silver,iron, nickel or nickel phosphorus. The shape of the leadframe 50 is notlimited to any size or geometric shape. The leadframe 50 may have beenmanufactured by punching a metal plate.

As illustrated in FIG. 10B, the semiconductor chip 30 (FIG. 10A) isplaced over the die pad 51. In the present embodiment the semiconductorchip 30 is mounted on the die pad 51 with the chip electrodes 21 facingaway from the die pad 51. The semiconductor chip 30 may be attached tothe die pad 51 by using an appropriate adhesive material.

It is to be noted that the semiconductor chip 30 may be produced by anyof the aforementioned methods. In particular, the semiconductor chip 30may be manufactured by one of the methods illustrated in FIGS. 7A to 7Eand FIGS. 8A to 8E, with the step of attaching the solder deposits 26being omitted.

As illustrated further in FIG. 10B, the chip electrodes 21 may beconnected to lead 52 of the leadframe 50 by wire-bonding. Inwire-bonding the tip of a bond-wire 53 is pressed by wire-bonding toolagainst the chip electrode 21 of the semiconductor chip 30 and heatand/or ultrasonic energy is applied to create a metallic connection. Thewire-bonding tool next extends the wire 53 to a bonding pad on theleadframe 50 and makes a “stitch” bond to that pad.

As illustrated in FIG. 10C, the wire-bonded structure shown in FIG. 10Bmay be placed in a mold tool 60. The mold tool 60 may comprise a lowerhalf 61 and an upper half 62. The lower half 61 and the upper half 62are brought together and closed, with the halves 61 and 62 defining acavity 63 in which the structure shown in FIG. 10B is accommodated. Theupper half 62 may have a dome or post 64 which is pressed on the topsurface of the plastic material 3. Except the abutment of the dome orpost 64 onto the top surface of the plastic material 3 and the lead 52of the leadframe 50 fixed by the mold tool, the structure shown in FIG.10A may have no peripheral areas which are in contact to walls of thecavity 63. Thus, the semiconductor chip 30, the insulating layer 23, thechip electrodes 21, exposed parts of the graphene layer 2, if any, andthe plastic material 3 are completely over-molded by the encapsulatingmaterial introduced into the cavity 63. This process may be accompaniedby the application of heat and pressure. After curing, the encapsulatingmaterial is rigid and forms an encapsulation body 65 (FIG. 10D). Theencapsulation body 65 has an opening 17 conforming to the shape of thepost or dome 64 of the upper mold half 62, with the opening 17 exposinga central part of the plastic material 3. The opening 17 may havelateral dimensions which are equal or smaller than the distance betweenthe chip electrodes 21. As illustrated in FIG. 10D, the encapsulationbody 65 may also completely cover the bottom of the semiconductor chip30 and the side faces of the semi-conductor chip 30. Thus, thesemiconductor chip 30 may be hermetically sealed by the encapsulationbody 65 and the plastic material 3 and the leads 52 are the only membersof the structure shown in FIG. 10B which are exposed by or protrude outof the encapsulation body 65.

As illustrated in FIG. 11, the structure shown in FIG. 10A may also bemounted on a leadframe 50 in a flip-chip orientation. To that end, thestructure shown in FIG. 10A is equipped with solder deposits 26 to forma device similar to the sensor device 200 as illustrated in FIG. 7E. Thesensor device 200 is then mounted on the leadframe 50, e.g., by a solderreflow process. Subsequently, the sensor device 200 mounted on theleadframe 50 is placed in a mold tool for fabricating the encapsulationbody 67. The molding tool is similar to the molding tool 60 as shown inFIG. 10C, with the exception that the dome or post 64 forms part of thelower mold half 61 rather than the upper mold half 62 and passes anopening between leads 52 of the leadframe 50. The manufacturing processof the sensor device 400 illustrated in FIG. 11 may be identical to themanufacturing process explained above in conjunction with FIGS. 10A to10D. Further, similar to the sensor device 300 illustrated in FIG. 10D,the encapsulation body 67 of the sensor device 400 may completelyencapsulate the chip 30, the chip electrodes 21, the insulating layer23, the graphene layer 2 (if not yet covered by the plastic material 3)and the plastic material 3 except a central surface portion thereof.Again, the dimension of the opening 17 of the encapsulation body toexpose the central portion of the plastic material 3 may be equal orsmaller than the distance between the chip electrodes 21.

FIG. 12 illustrates one embodiment of a sensor device 500 in across-sectional view. The sensor device 500 uses a leadless package suchas, e.g., a so-called TSLP (Thin Small Leadless Package). Such type ofpackage may comprise a carrier containing a metal chip pad 502 and metalcontact pads 503, 504 spaced apart and electrically insulated to eachother by polymer material 505. Compared to conventional leadframetechniques, in which leads or contact pads are typically structured bypunching or etching, the structuring method used in leadless packagesallows for a considerably higher packaging density. Further, the designvariability is enhanced, because the pads 502, 503, 504 may be insular,whereas in conventional leadframe technique, each contact pad or leadhas to be suspended at the frame structure of the leadframe.

A structured insulating layer 510 may extend on the carrier 502, 503,504, 505 and may cover zones between the chip pad 502 and the contactpads 503, 504. The structured insulating layer 510 may be used as asupporting basis for conducting lines 511 electrically connecting to thecontact pads 503, 504, the graphene layer 2 and, possibly, to chipelectrodes (not illustrated). The arrangement of the graphene layer 2and the plastic material 3 is similar to embodiments described beforeand will be omitted for the sake of brevity.

FIGS. 13A to 13M schematically illustrate a method of manufacturing asensor device 600, a cross-section of which is shown in FIG. 15. Themethod shown in FIGS. 13A to 13M is an implementation of the methodshown in FIGS. 1A to 1C. The details of the production method, that aredescribed below, can therefore be likewise applied to the method ofFIGS. 1A to 1C. Vice versa, the description of the processing stepsdescribed in conjunction with FIGS. 1A to 1C may be applied to themethod explained below with reference to FIGS. 13A to 13M.

As illustrated in FIG. 13A, a semiconductor wafer may include a bulksilicon in which integrated circuits are embedded. Chip electrodes 21may comprise first chip electrodes 21 a and second chip electrodes 21 b.The chip electrodes 21 a and 21 b may be made of metal, for example,aluminum or copper or any other metal mentioned above with reference tochip electrode 21.

According to FIG. 13B, an insulating layer 23 is deposited on the firstmain face 22 of the wafer 20. The insulating layer 23 may, for example,be made of the same materials as mentioned above with reference to otherembodiments. Thus, in particular, the insulating layer 23 may be apolymer layer or a hard passivation layer or a layer composed of a lowerhard passivation layer and an upper polymer layer.

As illustrated in FIG. 13B, the insulating layer 23 is structured toexpose the first chip electrodes 21 a and the second chip electrodes 21b. All method steps mentioned before to structure the insulating layer23 may be applied.

As illustrated in FIG. 13C, the semiconductor wafer 20 may then besingulated into the semiconductor chips 30, for example, by sawing,cutting, etching or laser ablation.

In order to package the semiconductor chips 30, a temporary carrier 80is provided as illustrated in FIG. 13D. The temporary carrier 80 may bea plate of a rigid material, for example, a metal, such as nickel, steelor stainless steel, laminate, film or a material stack. The temporarycarrier 80 may have at least one flat surface on which the semiconductorchips 30 may be placed. An adhesive tape 81, for example, a double-sidedsticky tape, may be laminated on the temporary carrier 80.

As illustrated in FIG. 13E, the semiconductor chips 30 are mounted onthe temporary carrier 80. The semiconductor chips 30 can be fixed on theadhesive tape 81. For attaching the semiconductor chips 30 to thetemporary carrier 80, other kinds of attaching materials or devices suchas, e.g., vacuum holders may alternatively be used.

As shown in FIG. 14, the semiconductor chips 30 may be arranged in anarray, with the semiconductor chips 30 being spaced apart from eachother in a certain distance. The temporary carrier 80 may be round (seeFIG. 14) or square shaped. The temporary carrier 80 may have anyappropriate size, e.g., a diameter D of about 0.2 or 0.3 m or more.

Referring again to FIG. 13E, the semiconductor chips 30 may be arrangedover the temporary carrier 80 with their first main faces 22 containingthe first and second chip electrodes 21 a, 21 b facing the temporarycarrier 80. In this case, the insulating layer 23 may be in directcontact with the adhesive tape 81.

After the semiconductor chips 30 have been mounted on the temporarycarrier 80, they are encapsulated with an encapsulating material formingan encapsulation body 90 as illustrated in FIG. 13F. The encapsulatingmaterial may cover second main faces 29 of the semiconductor chips 30,which are opposite to the first main faces 22, and also the side faces28 of the semiconductor chips 30. The gaps between the semiconductorchips 30 are also filled with the encapsulating material. For example,the encapsulating material may be a duroplastic or film resetting moldmaterial. The encapsulating material may be based on an epoxy materialand may contain a filling material consisting of small particles ofglass (SiO₂) or other electrically insulating mineral filler materialslike Al₂O₃ or organic filler materials. The mold material may, forexample, be applied by compression molding, injection molding, granulatemolding, powder molding or liquid molding. The encapsulation body 90embedding the semiconductor chips 30 is also referred to as artificialwafer in the art.

Alternatively, the encapsulating material may be a polymer materialhaving the shape of an electrically insulating foil or sheet, which islaminated on top of the semiconductor chips 30 as well as the temporarycarrier 80. Also in this case the gaps between the semiconductor chips30 are filled with the polymer material. The polymer material may, forexample, be a prepreg (short for pre-impregnated fibers) that is acombination of a fiber mat, for example, glass or carbon-fibers, and aresin, for example, a duroplastic material. For the lamination of aprepreg the same or similar process steps can be used as in PCBmanufacturing.

The semiconductor chips 30 encapsulated in the encapsulation body 90 arethen released from the temporary carrier 80, and the adhesive tape 81 ispeeled from the encapsulating material and the insulating layer 23 asillustrated in FIG. 13G. The adhesive tape 81 may feature thermo-releaseproperties, which allow for the removal of the adhesive tape 81 during aheat treatment. The removal of the adhesive tape 81 from the temporarycarrier 80 is carried out at an appropriate temperature, which dependson the thermo-release properties of the adhesive tape 81 and is usuallyhigher than 150° C.

After the release of the temporary carrier 80 and the adhesive tape 81,the face of the insulating layer 23 facing away from the semiconductorchip 30 and the bottom surface of the encapsulation body 90 form asubstantially common plane P. As described below and illustrated inFIGS. 13H to 13K, a redistribution layer may be applied to the plane P.

A dielectric layer 91 may be deposited on the plane P as illustrated inFIG. 13H. The dielectric layer 91 may be fabricated in various ways. Forexample, the dielectric layer 91 may be deposited from a gas phase orfrom a solution, or can be laminated onto the surface of the plane P.Furthermore, thin-filmed technology methods may be used for theapplication of the dielectric layer 91. The dielectric layer 91 may befabricated from a polymer such as, e.g., parylene, photoresist material,imide, epoxy, duroplast, silicone, silicone nitride or an inorganic,ceramic-like material such as silicon-carbon compounds. The dielectriclayer 91 may also be omitted.

In order to make electrical contacts to the integrated circuits embeddedin the semiconductor chips 30, the dielectric layer 91 may be opened inareas where the first and second chip electrodes 21 a, 21 b are arrangedas illustrated in FIG. 13H. The openings 92 in the dielectric layer 91may, for example, be produced by using photolithographic methods and/oretching methods.

A metal layer 93 may be applied to the dielectric layer 91 and isstructured as illustrated in FIG. 13I. According to one embodiment, themetal layer 93 may be fabricated by a plating process. By way ofexample, in a first step, a seed layer (not shown) may be deposited onthe dielectric layer 91 and may be covered by a photoresist layer (notshown) structured by a photo-lithographic process. Subsequently theportion of the seed layer exposed by the photoresist layer may bereinforced by galvanic deposition of a metallic material. During thegalvanic deposition of the metallic material the seed layer is employedas an electrode. Copper or other metals or metal alloys may be plated onthe seed layer in the unmasked areas and to the desired height, which isusually greater than 3 μm. That way, metal electrodes 93 a and conductortraces 93 b may be fabricated. In the embodiment illustrated in FIG. 13Ithe metal electrodes 93 a electrically connect to the first chipelectrodes 21 a and the conductor traces 93 b electrically connect tothe second chip electrodes 21 b.

According to FIG. 13J, a dielectric layer 94 may be deposited on top ofthe metal layer 93. The dielectric layer 94 may be opened in certainareas to expose portions of the metal electrodes 93 a and portions ofthe conductor traces 93 b. The exposed portions of the conductor traces93 b serve as external contact pads. The exposed portions of the metalelectrodes 93 a serve as electrical contacts for the graphene layer 2 tobe electrically connected thereto. The dielectric layer 94 may beproduced by using the same or similar materials and processing steps asdescribed above in connection with the dielectric layer 91.

As illustrated in FIG. 13K, a structured graphene layer 2 is generatedto extend between the at least two electrical contacts formed by theexposed portions of the metal electrodes 93 a associated with onesemiconductor chip 30. The graphene layer 2 may be deposited andstructured by using the same or similar materials and processing stepsas described above in connection with previous embodiments. Thestructured graphene layer 2 may directly overlay the dielectric layer 94in its peripheral region, may directly overlay the dielectric layer 91in its central region and may directly connect to the metal electrodes93 a in a region between the peripheral region and the central region.

As illustrated in FIG. 13L, the plastic material 3 is then deposited onthe graphene layer 2. The plastic material 3 may be deposited andstructured by using the same or similar materials and processing stepsas described above in connection with the foregoing embodiments. Inparticular, the plastic material 3 may either be deposited on apre-structured graphene layer 2 in accordance with the embodimentsillustrated in FIGS. 7A to 7E or the plastic material 3 may be depositedon the unstructured graphene layer 2 and utilized as a mask to structurethe graphene layer 2 as described in the embodiment of FIGS. 8A to 8E.

Solder deposits 26 may be placed on external contact pads provided bythe exposed portions of the conductor traces 93 b as illustrated in FIG.13M. The solder deposits 26 may be applied by so-called “ball placement”or other methods such as, e.g., stencil printing followed by aheat-treatment process. The solder deposits 26 may, for example, be madeof the materials mentioned before and may be used to electrically couplethe device 600 illustrated in FIG. 15 to other components, for example,a PCB.

As illustrated in FIG. 13M by the dashed separation line, the devices600 are separated from one another by separation of the encapsulationbody 90 and possibly the redistribution structure of layers 91, 93, 94,for example, by sawing, cutting, etching or a laser beam.

The sensor devices 600 (FIG. 15) manufactured by the method describedabove is the finished sensor device, and is also referred to as anembedded wafer level package in the art. Such packages may be fan-outtype packages. That is, the encapsulation body 90 allows theredistribution layer to extend beyond the outline of the semiconductorchip 30. The solder deposits 26 therefore do not need to be arrangedwithin the outline of the semiconductor chips 30, but can be distributedover a larger area. The increased area, which is available forarrangement of the solder deposits 26, means that the solder deposits 26may be arranged at a greater distance from one another and/or themaximum number of solder deposits 26 can be increased compared to thesituation when all the solder deposits 26 are arranged within theoutline of the semiconductor chips 30. By increasing the number ofexternal terminals (e.g., solder deposits 26) of the sensor device 600,the functionality and performance of the sensor device 600 may beenhanced. By way of example, the integrated circuit in the semiconductorchip 30 may be configured to have enhanced functionality such asprocessor functionality, logic functionality, memory functionality, etc.

The sensor devices of all embodiments described herein may be used,e.g., for the detection of fluids such as gases or liquids, inparticular nitrogen oxide, carbon dioxide, carbon monoxide, hydrogensulfite, methane, etc. Further, all these sensor devices may be used,e.g., as indoor-air-quality sensors, sensors for controlling acombustion engine, explosive agent detectors, selective fire detectors,etc.

In addition, while a particular feature or aspect of an embodiment ofthe invention may have been disclosed with respect to only one ofseveral implementations, such feature or aspect may be combined with oneor more other features or aspects of the other implementations as may bedesired and advantageous for any given or particular application.Furthermore, to the extent that the terms “include”, “have”, “with”, orother variants thereof are used in either the detailed description orthe claims, such terms are intended to be inclusive in a manner similarto the term “comprise”. Furthermore, it should be understood thatembodiments of the invention may be implemented in discrete circuits,partially integrated circuits or fully integrated circuits orprogramming means. Also, the term “exemplary” is merely meant as anexample, rather than the best or optimal. It is also to be appreciatedthat features and/or elements depicted herein are illustrated withparticular dimensions relative to one another for purposes of simplicityand ease of understanding, and that actual dimensions may differsubstantially from that illustrated herein.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat a variety of alternate and/or equivalent implementations may besubstituted for the specific embodiments shown and described withoutdeparting from the scope of the present invention. This application isintended to cover any adaptations or variations of the specificembodiments discussed herein. Therefore, it is intended that thisinvention be limited only by the claims and the equivalents thereof.

What is claimed is:
 1. A sensor device comprising: a substrate; agraphene layer disposed over the substrate; a plastic material disposedover the graphene layer; electrical contacts coupled to the graphenelayer; and an encapsulation body disposed over the plastic material,wherein the encapsulation body comprises an opening exposing the plasticmaterial.
 2. The sensor device of claim 1, wherein the encapsulationbody comprises a molded encapsulating material.
 3. The sensor device ofclaim 2, wherein the molded encapsulating material comprises aduroplastic, a film resetting mold material or an epoxy material.
 4. Thesensor device of claim 1, wherein the substrate comprises an integratedcircuit configured to measure an electrical resistance between theelectrical contacts coupled to the graphene layer.
 5. The sensor deviceof claim 1, wherein the plastic material disposed over the graphenelayer comprises the plastic material partially disposed over thegraphene layer.
 6. The sensor device of claim 1, wherein the plasticmaterial comprises polyethylenterephtalate.
 7. The sensor device ofclaim 1, wherein the plastic material comprises polyvinylidene.
 8. Thesensor device of claim 1, wherein the electrical contacts are spacedapart from each other and are disposed on an upper surface of thegraphene layer.
 9. The sensor device of claim 1, wherein the electricalcontacts are spaced apart from each other and are disposed on a lowersurface of the graphene layer.
 10. An arrangement comprising: aleadframe; and a sensor device comprising: a substrate; a graphene layerdisposed over the substrate; a plastic material disposed over thegraphene layer; electrical contacts coupled to the graphene layer,wherein the electrical contacts of the sensor device are electricallyconnected to the leadframe; and an encapsulation body accommodating theleadframe, the substrate, the graphene layer and the plastic material,wherein the encapsulation body comprises an opening exposing the plasticmaterial.
 11. The arrangement of claim 10, wherein the electricalcontacts of the sensor device are electrically connected to theleadframe via solder connections.
 12. The arrangement of claim 10,wherein the electrical contacts of the sensor device are electricallyconnected to the leadframe via bond wires.
 13. The arrangement of claim10, wherein the encapsulation body accommodates a portion of theleadframe.
 14. The arrangement of claim 10, wherein the encapsulationbody comprises a molded encapsulating material.
 15. The arrangement ofclaim 14, wherein the molded encapsulating material comprises aduroplastic, a film resetting mold material or an epoxy material. 16.The arrangement of claim 10, wherein the plastic material comprisespolyethylenterephtalate.
 17. The arrangement of claim 10, wherein theplastic material comprises polyvinylidene.